<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text">
<input type="button" value="平方" onclick="f()">
<input type="button" value="求和" onclick="f1()">

<div>结果</div>
<script>

        let d=document.querySelector("div");
        let i=document.querySelector("input");
        function f1() {
            //d.innerText="结果:"+(i.value*1+i.value*1);
            d.innerText="结果:"+(parseFloat(i.value)+parseFloat(i.value));
        }


        function  f(){
        if(isNaN(i.value)){
            d.innerText="输入结果错误!"
            return
        }

        d.innerText="结果:"+i.value*i.value;
    }

</script>

</body>
</html>